Ablation therapy is utilized throughout the body to disrupt unwanted tissues of a patient. In one example, ablation catheters can be used to create tissue necrosis to treat a variety of health conditions, including cardiovascular conditions such as cardiac arrhythmias. A common cause of cardiac arrhythmias is the abnormal routing of electricity through the cardiac tissue. Thus, arrhythmias can be treated by ablating suspected areas of electrical misfiring, thereby inactivating such aberrant firing. An ablation catheter can apply ablative energy (e.g., without limitation, radiofrequency (RF) energy, cryoablation, lasers, chemicals, high-intensity focused ultrasound (HIFU)) to target tissues to purposefully create lesions in an effort to disrupt undesirable electrical and/or neural pathways to limit or prevent the aberrant signals that lead to the underlying conditions. In some instances, the ablation catheter ablates sufficient target and surrounding tissue to create non-conductive barriers to the progression of aberrant electrical activity through the cardiac tissue. In particular, ablation therapy using RF waves on cardiac tissue is used to cure a variety of cardiac arrhythmias such as, without limitation, supraventricular tachycardia, Wolff-Parkinson-White syndrome (WPW), ventricular tachycardia, atrial fibrillation, atrial flutter, and ectopic atrial tachycardia.
The ablative energy must be directed such that the target tissue is ablated without unduly injuring the surrounding tissue. In some instances, the ablation procedure can cause undesirable charring of adjacent tissue and localized coagulation. A difficulty associated with ablation procedures stems from a healthcare provider's lack of real-time knowledge over the size, shape, and depth of the treated region. Such uncertainty can make it difficult for the healthcare provider to monitor the degree to which the tissue has been ablated, which makes it difficult to determine when to stop, reduce, or redirect the application of ablative energy.
Currently, lesions are evaluated following the ablation procedure. In some instances following a cardiac ablation procedure, a physician will evaluate the lesions through electrophysiologic mapping by positioning a catheter in the heart to measure the remaining electrical activity and determine whether the lesions have created a nonconductive pathway that is adequately halting aberrant conductivity. Conventional mapping techniques used during ablation procedures require the clinician to manually mark treated regions on an anatomical map. If it is established that the lesions were inadequately formed, then additional lesions may be created to complete the nonconductive pathway and address the aberrant conductivity. However, this post-ablation evaluation entails further medical procedures and extends the time required to treat the patient's underlying condition. Moreover, the anatomical marking may be affected by numerous variables, including movement of the target tissue and/or the catheter due to cardiac contractions and ventilation. Thus, there may not be strong correlation between the lesions marked on the anatomical map and the effective delivery of ablative therapy.
One method of evaluating lesions as they are formed is to measure the electrical impedance and/or the temperature of the target tissue and surrounding tissues. Biochemical differences between ablated and normal tissues can result in changes in electrical impedance between the tissue types. In general, impedance measurements are roughly correlated with impedance measurements. Though impedance is routinely monitored during electrophysiologic therapy, however, it is not directly related to lesion formation. Measuring impedance provides data as to the location of the ablated tissue, but it does not provide any qualitative, real-time data about the character of the ablated tissue to enable evaluation of the effectiveness of the lesion or the degree of ablation.
Another approach is lesion pacing, where the healthcare provider can measure the electrical conductance between two points of tissue bridging the lesion. However, lesion pacing only measures the effectiveness of the lesion in creating a nonconductive area. It does not provide any qualitative data about the character of the ablated tissue or the degree of ablation.
The devices, systems, and methods disclosed herein overcome one or more of the deficiencies of the prior art.